1. Field of the Invention
This invention relates to an improved method for preparing stretchable multi-layer composite sheets wherein at least one layer in the multilayer composite sheet comprises multiple-component spirally-crimped fibers.
2. Description of the Related Art
Nonwoven webs made from multiple-component filaments are known in the art. The products are usually heavy, with high-loft, and the fibers are highly bonded at their cross-over points. For example, U.S. Pat. No. 3,595,731 to Davies et al. (Davies) describes bicomponent fibrous materials containing crimped fibers which are bonded mechanically by the interlocking of the spirals in the crimped fibers and adhesively by melting of a low-melting adhesive polymer component. The crimp can be developed and the potentially adhesive component activated in a single treatment step, or the crimp can be developed first followed by activation of the adhesive component to bond together fibers of the web which are in a contiguous relationship. The crimp is developed under conditions where no appreciable pressure is applied during the process that would prevent the fibers from crimping.
U.S. Pat. No. 5,102,724 to Okawahara et al. (Okawahara) describes the finishing of nonwoven fabrics comprising bicomponent polyester filaments produced by conjugate spinning of side-by-side filaments of polyethylene terephthalate copolymerized with a structural unit having a metal sulfonate group and a polyethylene terepthalate or a poly(1,4-butylene terephthalate). The filaments are mechanically crimped prior to forming a nonwoven fabric. The fabric is rendered stretchable by exposure to infrared radiation while the filaments are in a relaxed state. During the infrared heating step, the conjugate filaments develop three dimensional crimp and high-loft.
U.S. Pat. No. 5,382,400 to Pike et al. (Pike) describes a process for making a nonwoven fabric which includes the steps of melt-spinning continuous multiple-component polymeric filaments, drawing the filaments, at least partially quenching the multiple-component filaments so that the filaments have latent helical (spiral) crimp, activating the latent helical crimp, and thereafter forming the crimped continuous multiple-component filaments into a nonwoven fabric. The resulting nonwoven fabric is described as being substantially stable and uniform and can have high loft.
PCT Published Application No. WO 00/66821 describes stretchable nonwoven webs which comprise a plurality of bicomponent fibers that can also be blended with non-bicomponent fibers which are point-bonded prior to heating to develop crimp in the filaments. The bicomponent filaments comprise a polyester component and another polymeric component that is preferably a polyolefin or polyamide. The heating step causes the bonded web to shrink resulting in a nonwoven fabric which exhibits elastic recovery in both the machine direction and the cross direction when stretched up to 30%.
Multi-layer composite elastic nonwoven materials are also known in the art. Examples of multi-layer elastic nonwoven materials include “stretch-bonded” and “neck-bonded” laminates. Stretch-bonded laminates are prepared by joining a gatherable layer to an elastic layer while the elastic layer is in an extended condition so that upon relaxing the layers, the gatherable layer is gathered. “Neck-bonded laminates” are produced by joining a necked, non-elastic layer with an elastic layer when the non-elastic layer is in an extended condition. The elastic layer generally comprises an elastic film or an elastic nonwoven web. Preparation of these composite nonwoven materials requires that one of the layers be in an extended condition prior to combining with the second layer. When elastic films are used as the elastic layer, the elastic composite materials are generally unsuitable for some apparel end uses due to the high retractive power of the elastic films.
U.S. Pat. No. 3,671,379 to Evans et al. (Evans) describes self-crimpable composite filaments which comprise a laterally eccentric assembly of at least two synthetic polyesters, the first of said two polyesters being partly crystalline in which the chemical repeat-units of its crystalline region are in a non-extended stable conformation and the second of said two polyesters being partly crystalline in which the chemical repeat-units of the crystalline region are in a conformation more closely approaching the length of the conformation of its fully extended chemical repeat-units. The composite filaments are capable of developing a high degree of helical crimp against the restraint imposed by high thread count woven structures, which crimp potential is unusually well retained despite application of elongating stress and high temperature. The composite filaments increase, rather than decrease, in crimp potential when annealed under tension as a part of the fiber production process. The filaments are described as being useful in knitted, woven, and nonwoven fabrics.
Stretchable nonwoven fabrics comprising spirally-crimped multiple-component fibers known in the art generally have poor hand due to the presence of the spirally-crimped fibers on the nonwoven fabric surface which contributes to surface harshness, pilling, etc. This is true even when the spirally-crimped fibers are blended with other textile fibers such as cotton, rayon, microfibers such as sub-denier polyester or nylon, polyethylene, polypropylene, etc. The desirable properties characteristic of these other textile fibers such as soft hand, absorbency, repellency, dye uniformity, etc. are diluted by blending with the spirally-crimped fibers. Nonwoven fabrics known in the art which contain spirally-crimped fibers blended with other fibers generally have limited use as home furnishing fabrics, apparel, etc. because of the relatively harsh surface created by the fully activated spirally-crimped fibers, and other blended surface properties described above.
There remains a need for low cost stretchable composite sheets such as multi-layer nonwoven fabrics which are strong, durable, and uniform and which have an improved combination of surface qualities, strength, uniformity, and drape for end uses such as apparel and home furnishings. It is further desirable to reduce the complexity of the manufacturing process by providing a process for preparing elastic composite sheets which does not require that one of the layers be in an extended state during the manufacturing process.